Spectra of the water isotopologues in comet 46P/Wirtanen. The 1_1, 0 − 1_0, 1 and HDO transitions are shown in the upper and lower panels, respectively. The intensity scale is the main beam brightness temperature. The spectral resolution is 0.24 MHz, corresponding to approximately 0.14 km s⁻¹. A Gaussian fit to the spectrum (green line, upper panel) gives a line center velocity ν_o = 0.08 ± 0.04 km s⁻¹ and a full width at half maximum line width Δν = 1.09 ± 0.09 km s⁻¹. Vertical dotted lines indicate the velocity range used in computations of the integrated line intensities (–1.04 to 1.2 km s⁻¹). The green line in the lower panel shows the expected HDO line intensity assuming D/H equal to VSMOW. The inset in the upper panel shows the evolution of the integrated line intensity as a function of UT time. Error bars include statistical and calibration uncertainties, combined in quadrature, and the gray shaded area shows the corresponding uncertainty on the average line intensity (ensemble average).